E-UTRA Downlink and Uplink Carrier Frequencies
Evolved universal terrestrial radio access (E-UTRA) uses orthogonal frequency division multiplexing (OFDM) in downlink (DL) transmission and single carrier frequency division multiple access (SC-FDMA) in the uplink (UL). The center frequency of the DL bandwidth and the UL bandwidth is called carrier frequency. The subcarrier spacing for both DL and the UL is equal to 15 kHz.
In order to limit the magnitude of the signal which causes inefficiency in the digital to analog (D/A) and analog to digital (A/D) converters, the direct current (DC) subcarrier in the DL is usually not used for transmission and is set to zero. In the baseband signal this subcarrier corresponds to frequency zero, which means a DC component in the baseband signal.
To avoid the similar problem in the UL, the subcarriers are shifter by 7.5 kHz to avoid transmission on the center frequency and also to save the number of subcarriers. FIG. 1A for example illustrates subcarrier arrangements in the DL and UL in the legacy E-UTRA standard.
The carrier frequency in the uplink and downlink is designated by the E-UTRA Absolute Radio Frequency Channel Number (EARFCN) in the range 0-262143. The relation between EARFCN and the carrier frequency in MHz for the downlink is given by the following equation, where FDL_low and NOffs-DL are given in Table 5.7.3-1 of 3GPP technical specifications 36.101 and 36.104 (as shown in FIGS. 1B-1C), and NDL is the downlink EARFCN.FDL=FDL_low+0.1(NDL−NOffs-DL)
The relation between EARFCN and the carrier frequency in MHz for the uplink is given by the following equation where FUL_low and NOffs-UL are given in Table 5.7.3-1 of 3GPP technical specifications 36.101 and 36.104, and NUL is the uplink EARFCN.FUL=FUL_low+0.1(NUL−NOffs-UL)E-UTRA Out of Band Emission
The out of band emissions are unwanted emissions immediately outside the assigned channel bandwidth resulting from the modulation process and non-linearity in the transmitter but excluding spurious emissions. This out of band emission limit is specified in terms of a spectrum emission mask and an Adjacent Channel Leakage power Ratio (ACLR).
The spectrum emission mask applies to frequencies (ΔfOOB) starting from the ±edge of the assigned E-UTRA channel bandwidth. As an example, for E-UTRA user equipment (UE) the emission should not exceed the levels specified in Table 1 shown in FIG. 2 for the specified channel bandwidth.
Narrow Band Internet of Things (NB-IoT)
In GERAN #62, a study item on “Cellular System Support for Ultra Low Complexity and Low Throughput Internet of Things” was approved. The aim was to study both the possibility of evolving current Global System for Mobile communications (GSM) Enhanced Data Rates for GSM Evolution (EDGE) Radio Access Network (GERAN) system and the design of a new access system towards low complexity and low throughput radio access technology to address the requirements of cellular internet of things. The objectives of the study were: improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and (optimized) network architecture. As per the PCG #34 decisions, it was agreed to move the normative phase of a single “clean-slate solution” to 3GPP Long Term Evolution (LTE). This feature is called Narrowband Internet of Things (NB-IOT).
3GPP LTE represents the project within the third generation partnership project, with an aim to improve the UMTS (Universal Mobile Telecommunications Service) standard. 3GPP LTE radio interface offers high peak data rates, low delays and increase in spectral efficiencies. LTE ecosystem supports both Frequency division duplex (FDD) and Time division duplex (TDD). This enables the operators to exploit both the paired and unpaired spectrum since LTE has flexibility in bandwidth as it supports 6 bandwidths 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz.
The objective of this new work item on NB-IOT is to specify a radio access for cellular internet of things, based to a great extent on a non-backward-compatible variant of E-UTRA, that addresses improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra low device cost, low device power consumption and (optimized) network architecture.
NB-IoT should support 3 different modes of operation: (1) ‘Stand-alone operation’ utilizing for example the spectrum currently being used by GERAN systems as a replacement of one or more GSM carriers. In principle it operates on any carrier frequency which is neither within the carrier of another system not within the guard band of another system's operating carrier. The other system can be another NB-IOT operation or any other RAT e.g. LTE. (2) ‘Guard band operation’ utilizing the unused resource blocks within a LTE carrier's guard-band. The term guard band may also interchangeably be called guard bandwidth. (3) ‘In-band operation’ utilizing resource blocks within a normal LTE carrier. The in-band operation may also interchangeably be called in-bandwidth operation.
In NB-IoT, the downlink transmission is based on OFDM with 15 kHz subcarrier spacing for all the scenarios: standalone, guard-band, and in-band. For UL transmission, both multi-tone transmissions based on SC-FDMA, and single tone transmission is supported. A multi-tone transmission is based on SC-FDMA with 15 kHz UL subcarrier spacing. For the single tone transmissions, two numerologies can be configurable by the network 3.75 kHz and 15 kHz. A cyclic prefix is inserted.
This means that the physical waveforms for NB-IoT in downlink and also partly in uplink is similar to legacy LTE.
In the downlink design, NB-IoT supports both master information broadcast and system information broadcast which are carried by different physical channels. For in-band operation, it is possible for NB-IoT UE to decode the narrowband physical broadcast channel (NB-PBCH) without knowing the legacy physical resource block (PRB) index. NB-IoT supports both downlink physical control channel (NB-PDCCH) and downlink physical shared channel (PDSCH). The operation mode of NB-IoT must be indicated to the UE, and currently 3GPP is considering indication by means of NB-SSS (secondary synchronization signal), NB-MIB (master information block) or perhaps other downlink signals.
NB-IoT supports physical broadcast channel (NPBCH), physical downlink control channel (NPDCCH), physical downlink shared channel (PDSCH), physical uplink control channel (NPUCCH), physical uplink shared channel (NPUSCH), physical random access channel (NPRACH).
The general design principle of NB-IoT follows that of legacy LTE. Downlink synchronization signal consists of primary synchronization signal (NPSS) and secondary synchronization signal (NSSS). The periodicity of NPSS transmission is 10 ms.
Also cell specific reference symbols (NRS) are defined for NB-IoT. FIG. 3 shows the NRS reference symbols for different operation modes; namely, for NB-IoT in-band and guardband/stand-alone scenarios.
Channel Arrangement in NB-IoT
The channel raster for all operation modes of NB-IoT is 100 kHz. However, the carrier frequency of an NB-IoT channel may be at an offset compared to the 100 kHz grid. For example, as shown in FIG. 4, in case of guard-band operation in 10 MHz system bandwidth the first PRBs adjacent to the PRBs 0-49 within the LTE transmission bandwidth are centered at 4597.5 kHz and −4597.5 kHz.
FIG. 5 shows a table with the center frequency offset for the adjacent PRB in the higher frequency guard band for different LTE system bandwidths. The offset is the same to the adjacent PRB in the lower guard band. The 1.4 MHz system bandwidth has been excluded since guard band operation is not seen as feasible. It can be seen that the center frequency of the guard band PRB is at multiples of 2.5 kHz off the 100 kHz frequency raster. It has been agreed in 3GPP that the DL and UL center frequency of the NB-IoT can be described asFDL=FDL_low+0.1(NDL−NOffs-DL)+0.0025*(2MDL+1)  (1)FUL=FUL_low+0.1(NUL−NOffs-UL)+0.0025*(2MUL)  (2)where NDL and NUL are E-UTRA Absolute Radio Frequency Channel Number (EARFCN). MDL and MUL are the offset of NB-IoT channel to the raster andMDL∈{−10,−9,−8,−7,−6,−5,−4,−3,−2,−1,−0.5,0,1,2,3,4,5,6,7,8,9},MUL∈{−10,−9,−8,−7,−6,−5,−4,−3,−2,−1,0,1,2,3,4,5,6,7,8,9}.
It has also been agreed that the UL frequency carrier is to be determined as follows for all deployment scenarios. For initial access, the NB-IoT DL/UL frequency separation is configured by higher layers (SIBx) and is cell-specific. After the initial random access procedure success, there can also be a UE specific configuration for the NB-IoT DL/UL frequency separation.
This means that based on the network signaling, the spacing between the TX and RX may be fixed or may be variable.
NB-IoT Out of Band Emission
The spectrum emission mask of NB-IoT UE applies to frequencies (ΔfOOB) starting from the ±edge of the assigned NB-IoT UE channel bandwidth. The power of any category NB1 UE emission shall not exceed the levels specified in the table shown in FIG. 6.
The Background section of this document is provided to place embodiments of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.